Newton's laws of motion
Newton's laws of motion are three physical laws that form the basis for classical mechanics. They have been expressed in several different ways over nearly three centuries,For explanations of Newton's laws of motion by Newton in the early 18th century, by the physicist William Thomson (Lord Kelvin) in the mid-19th century, and by a modern text of the early 21st century, see:- # Newton's "Axioms or Laws of Motion" starting on page 19 of volume 1 of the 1729 translation of the "Principia"; # [http://books.google.com/books?id=wwO9X3RPt5kC&pg=PA178 Section 242, Newton's laws of motion] in Thomson, W (Lord Kelvin), and Tait, P G, (1867), Treatise on natural philosophy, volume 1; and # [[#cro2000|Benjamin Crowell (2000), Newtonian Physics]]. and can be summarised as follows: # In the absence of a net force, the center of mass of a body either is at rest or moves at a constant velocity. # A body experiencing a force F''' experiences an acceleration '''a related to F''' by '''F = m'a', where m'' is the mass of the body. Alternatively, force is equal to the time derivative of momentum. # Whenever a first body exerts a force '''F' on a second body, the second body exerts a force −'F' on the first body. F''' and −'''F are equal in magnitude and opposite in direction. These laws describe the relationship between the forces acting on a body and the motion of that body. They were first compiled by Sir Isaac Newton in his work Philosophiæ Naturalis Principia Mathematica, first published on July 5, 1687.See the Principia on line at Andrew Motte Translation Newton used them to explain and investigate the motion of many physical objects and systems.[http://members.tripod.com/~gravitee/axioms.htm Andrew Motte translation of Newton's Principia (1687) Axioms or Laws of Motion] For example, in the third volume of the text, Newton showed that these laws of motion, combined with his law of universal gravitation, explained Kepler's laws of planetary motion. Definitions .]] Newton's laws of motion are often defined as: * First Law: An object at rest tends to stay at rest, or if it is in motion tends to stay in motion with the same speed and in the same direction unless acted upon by a sum of physical forces. * Second Law: A body will accelerate with acceleration proportional to the force and inversely proportional to the mass. * Third Law: Every action has a reaction equal in magnitude and opposite in direction. Explanation ;First law :There exists a set of inertial reference frames relative to which all particles with no net force acting on them will move without change in their velocity. Newton's first law is often referred to as the law of inertia. ;Second law :Observed from an inertial reference frame, the net force on a particle is equal to the time rate of change of its linear momentum: F''' = d(''mv')/d''t''. Since by definition the mass of a particle is constant, this law is often stated as, "Force equals mass times acceleration (F''' = ''ma'): the net force on an object is equal to the mass of the object multiplied by its acceleration." ;Third law :Whenever a particle A'' exerts a force on another particle ''B, B'' simultaneously exerts a force on ''A with the same magnitude in the opposite direction. The strong form of the law further postulates that these two forces act along the same line. Newton's third law is sometimes referred to as the action-reaction law. In the given interpretation mass, acceleration, momentum, and (most importantly) force are assumed to be externally defined quantities. This is the most common, but not the only interpretation: one can consider the laws to be a definition of these quantities. Some authors interpret the first law as defining what an inertial reference frame is; from this point of view, the second law only holds when the observation is made from an inertial reference frame, and therefore the first law cannot be proved as a special case of the second. Other authors do treat the first law as a corollary of the second. The explicit concept of an inertial frame of reference was not developed until long after Newton's death. At speeds approaching the speed of light the effects of special relativity must be taken into account.In making a modern adjustment of the second law for (some of) the effects of relativity, m'' would be treated as the relativistic mass, producing the relativistic expression for momentum, and the third law might be modified if possible to allow for the finite signal propagation speed between distant interacting particles. Newton's first law Lex I: Corpus omne perseverare in statu suo quiescendi vel movendi uniformiter in directum, nisi quatenus a viribus impressis cogitur statum illum mutare. '''Every body persists in its state of being at rest or of moving uniformly straight forward, except insofar as it is compelled to change its state by force impressed.'Isaac Newton, The Principia, A new translation by I.B. Cohen and A. Whitman, University of California press, Berkeley 1999. Newton's first law is also called the law of inertia. It states that if the vector sum of all forces (that is, the net force) acting on an object is zero, then the acceleration of the object is zero and its velocity is constant. Consequently: * An object that is at rest will stay at rest until an unbalanced force acts upon it. * An object that is in motion will not change its velocity until an unbalanced force acts upon it. In the first point, the phrase unbalanced force refers to a set of forces which do not have a zero sum (net force zero) or whose torques about the center of mass of the object do not have a zero sum. Indeed, without the torque requirement, a net force of zero will not accelerate the center of mass of an extended object, but may cause the object to rotate. The second point seems to violate everyday experience. For example, a hockey puck sliding along ice does not move forever; rather, it slows and eventually comes to a stop. According to Newton's first law, the puck comes to a stop because of a net external force applied in the direction opposite to its motion. This net external force is due to a frictional force between the puck and the ice, as well as a frictional force between the puck and the air. If the ice were frictionless and the puck were traveling in a vacuum, the net external force on the puck would be zero and it would travel with constant velocity so long as its path were unobstructed. Implicit in the discussion of Newton's first law is the concept of an inertial reference frame, which for the purposes of Newtonian mechanics is defined to be a reference frame in which Newton's first law holds true. Newton placed the law of inertia first to establish frames of reference for which the other laws are applicable. To understand why the laws are restricted to inertial frames, consider a ball at rest inside an airplane on a runway. From the perspective of an observer within the airplane (that is, from the airplane's frame of reference) the ball will appear to move backward as the plane accelerates forward. This motion appears to contradict Newton's second law (F''' = ''ma'), since, from the point of view of the passengers, there appears to be no force acting on the ball that would cause it to move. However, Newton's first law does not apply: the stationary ball does not remain stationary in the absence of external force. Thus the reference frame of the airplane is not inertial, and Newton's second law does not hold in the form F''' = ''ma'.Newton's laws can be made applicable in non-inertial frames through the addition of so-called fictitious forces. History of the first law Newton's first law is a restatement of what Galileo had already described and Newton gave credit to Galileo. It differs from Aristotle's view that all objects have a natural place in the universe. Aristotle believed that heavy objects like rocks wanted to be at rest on the Earth and that light objects like smoke wanted to be at rest in the sky and the stars wanted to remain in the heavens. However, a key difference between Galileo's idea and Aristotle's is that Galileo realized that force acting on a body determines acceleration, not velocity. This insight leads to Newton's First Law—no force means no acceleration, and hence the body will maintain its velocity. The law of inertia apparently occurred to several different natural philosophers and scientists independently. The inertia of motion was described in the 3rd century BC by the Chinese philosopher Mo Tzu, and in the 11th century by the Muslim physicists AlhazenAbdus Salam (1984), "Islam and Science". In C. H. Lai (1987), Ideals and Realities: Selected Essays of Abdus Salam, 2nd ed., World Scientific, Singapore, p. 179-213. and Avicenna.Fernando Espinoza (2005). "An analysis of the historical development of ideas about motion and its implications for teaching", Physics Education 40 (2), p. 141. The 17th century philosopher René Descartes also formulated the law, although he did not perform any experiments to confirm it. The first law was understood philosophically well before Newton's publication of the law.Thomas Hobbes wrote in Leviathan: ;Islamic precursors Ibn al-Haytham (965-1039) enunciated the law of inertia, later known as Newton's first law of motion, when he stated that a body moves perpetually unless an external force stops it or changes its direction of motion.Dr. Nader El-Bizri, "Ibn al-Haytham or Alhazen", in Josef W. Meri (2006), Medieval Islamic Civilization: An Encyclopaedia, Vol. II, p. 343-345, Routledge, New York, London. Nobel Prize winning physicist Abdus Salam wrote the following on Ibn al-Haytham: Avicenna (Ibn Sina) (980-1037), in The Book of Healing, developed an elaborate theory of motion, in which he made a distinction between the inclination and force of a projectile, and concluded that motion was a result of an inclination (mayl) transferred to the projectile by the thrower, and that projectile motion in a vacuum would not cease.Fernando Espinoza (2005). "An analysis of the historical development of ideas about motion and its implications for teaching", Physics Education 40 (2), p. 141 This was the first alternative to the Aristotelian theory. In the Avicennan theory of motion, the violent inclination he conceived was non-self-consuming, a permanent force whose effect was dissipated only as a result of external agents such as air resistance. He concluded that continuation of motion is attributed to the inclination that is transferred to the object, and that object will be in motion until the mayl is spent. He also claimed that projectile in a vacuum would not stop unless it is acted upon. This makes him "the first to conceive such a permanent type of impressed virtue for non-natural motion." Such a self-motion (mayl) is "almost the opposite of the Aristotelian conception of violent motion of the projectile type, and it is rather reminiscent of the principle of inertia, i.e., Newton's first law of motion"Aydin Sayili (1987), "Ibn Sīnā and Buridan on the Motion of the Projectile", Annals of the New York Academy of Sciences 500 (1): 477–482 477: states that an object in motion will stay in motion unless it is acted on by an external force. Avicenna's theory of motion was reminiscent of the later concept of inertia in classical mechanics, and later formed the basis of Jean Buridan's theory of impetus and exerted an influence on the work of Galileo Galilei.A. Sayili (1987), "Ibn Sīnā and Buridan on the Motion of the Projectile", Annals of the New York Academy of Sciences 500 (1), pp. 477–482 Averroes (1126–1198) developed the notion that bodies have a (non-gravitational) inherent resistance to motion into physics, an idea that was adopted by Thomas Aquinas and subsequently by Johannes Kepler who referred to it as 'inertia'.See e.g. Sorabji 1988 Matter,Space and Motion p284 In the early 16th century, al-Birjandi developed a hypothesis similar to Galileo's notion of "circular inertia." (See Earth's motion below.) Newton's second law Newton's second law states that the force applied to a body produces a proportional acceleration; the relationship between the two is : \mathbf{F} = m\mathbf{a} where F''' is the net force applied, m is the mass of the body, and '''a is the body's acceleration. If the body is subject to multiple forces at the same time, then the net force is the vector sum of the individual forces: : \mathbf{F} = \mathbf{F}_1 + \mathbf{F}_2 + \cdots + \mathbf{F}_n. The second law also states that the net force is equal to the time derivative of the body's momentum p': : \mathbf{F} = m\mathbf{a} = m\,\frac{\mathrm{d}\mathbf{v}}{\mathrm{d}t} = \frac{\mathrm{d}(m\mathbf v)}{\mathrm{d}t} = \frac{\mathrm{d}\mathbf{p}}{\mathrm{d}t} where, since the law is valid only for constant-mass systems, "We may conclude emphasizing that Newton's second law is valid for constant mass only. When the mass varies due to accretion or ablation, alternate equation explicitly accounting for the changing mass should be used." as in the original the mass can be taken inside the differentiation operator by the constant factor rule in differentiation. Any mass that is gained or lost by the system will cause a change in momentum that is not the result of an external force. A different equation is necessary for variable-mass systems (see below). Consistent with the first law, the time derivative of the momentum is non-zero when the momentum changes direction, even if there is no change in its magnitude (see time derivative). The relationship also implies the conservation of momentum: when the net force on the body is zero, the momentum of the body is constant. This can be said easily. Net force is equal to rate of change of momentum for those who are unfamiliar with calculus. Newton's second law requires modification if the effects of special relativity are to be taken into account, since it is no longer true that momentum is the product of inertial mass and velocity. Impulse An impulse I''' occurs when a force '''F acts over an interval of time Δ''t'', and it is given byHannah, J, Hillier, M J, Applied Mechanics, p221, Pitman Paperbacks, 1971 : \mathbf{I} = \int_{\Delta t} \mathbf F \,\mathrm{d}t . Since force is the time derivative of momentum, it follows that : \mathbf{I} = \Delta\mathbf{p} = m\Delta\mathbf{v}. This relation between impulse and momentum is closer to Newton's wording of the second law. Impulse is a concept frequently used in the analysis of collisions and impacts. Variable-mass systems Variable-mass systems, like a rocket burning fuel and ejecting spent gases, are not closed and cannot be directly treated by making mass a function of time in the second law. The reasoning, given in An Introduction to Mechanics by Kleppner and Kolenkow and other modern texts, is that Newton's second law applies fundamentally to particles. In classical mechanics, particles by definition have constant mass. In case of a well-defined system of particles, Newton's law can be extended by summing over all the particles in the system: : \mathbf{F}_{\mathrm{net}} = M\mathbf{a}_\mathrm{cm} where F'net is the total external force on the system, ''M is the total mass of the system, and 'a'cm is the acceleration of the center of mass of the system. Variable-mass systems like a rocket or a leaking bucket cannot usually be treated as a system of particles, and thus Newton's second law cannot be applied directly. Instead, the general equation of motion for a body whose mass m varies with time by either ejecting or accreting mass is obtained by rearranging the second law and adding a term to account for the momentum carried by mass entering or leaving the system: : \mathbf F + \mathbf{u} \frac{\mathrm{d} m}{\mathrm{d}t} = m {\mathrm{d} \mathbf v \over \mathrm{d}t} where '''u is the relative velocity of the escaping or incoming mass with respect to the center of mass of the body. Under some conventions, the quantity u' d''m/d''t'' on the left-hand side, known as the thrust, is defined as a force (the force exerted on the body by the changing mass, such as rocket exhaust) and is included in the quantity '''F. Then, by substituting the definition of acceleration, the equation becomes : \mathbf F = m \mathbf a. History of the second law Newton's Latin wording for the second law is: Lex II: Mutationem motus proportionalem esse vi motrici impressae, et fieri secundum lineam rectam qua vis illa imprimitur. This was translated quite closely in Motte's 1729 translation as: LAW II: The alteration of motion is ever proportional to the motive force impress'd; and is made in the direction of the right line in which that force is impress'd. According to modern ideas of how Newton was using his terminology,According to Maxwell in Matter and Motion, Newton meant by motion "the quantity of matter moved as well as the rate at which it travels" and by impressed force he meant "the time during which the force acts as well as the intensity of the force". See Harman and Shapiro, cited below. this is understood, in modern terms, as an equivalent of: :The change of momentum of a body is proportional to the impulse impressed on the body, and happens along the straight line on which that impulse is impressed. Motte's 1729 translation of Newton's Latin continued with Newton's commentary on the second law of motion, reading: If a force generates a motion, a double force will generate double the motion, a triple force triple the motion, whether that force be impressed altogether and at once, or gradually and successively. And this motion (being always directed the same way with the generating force), if the body moved before, is added to or subtracted from the former motion, according as they directly conspire with or are directly contrary to each other; or obliquely joined, when they are oblique, so as to produce a new motion compounded from the determination of both. The sense or senses in which Newton used his terminology, and how he understood the second law and intended it to be understood, have been extensively discussed by historians of science, along with the relations between Newton's formulation and modern formulations.See for example (1) I Bernard Cohen, "Newton’s Second Law and the Concept of Force in the Principia", in "The Annus Mirabilis of Sir Isaac Newton 1666–1966" (Cambridge, Massachusetts: The MIT Press, 1967), pages 143–185; (2) Stuart Pierson, "'Corpore cadente. . .': Historians Discuss Newton’s Second Law", Perspectives on Science, 1 (1993), pages 627–658; and (3) Bruce Pourciau, "Newton's Interpretation of Newton's Second Law", Archive for History of Exact Sciences, vol.60 (2006), pages 157-207; also an online discussion by G E Smith, in 5. Newton's Laws of Motion, s.5 of "Newton's Philosophiae Naturalis Principia Mathematica" in (online) Stanford Encyclopedia of Philosophy, 2007. ;Islamic precursors Ibn al-Haytham (965-1039) developed the concept of momentum,Seyyed Hossein Nasr, "The achievements of Ibn Sina in the field of science and his contributions to its philosophy", Islam & Science, December 2003. though he did not quantify this concept mathematically. Abū Rayhān al-Bīrūnī (973-1048) realized that acceleration is connected with non-uniform motion. He recognized that non-uniform motion is the result of acceleration. Avicenna's (980-1037) theory of mayl attempted to provide a quantitive relation between the weight and velocity of a moving body, resembling the concept of momentum. for which he is considered a pioneer of the concept of momentum.Seyyed Hossein Nasr, "Islamic Conception Of Intellectual Life", in Philip P. Wiener (ed.), Dictionary of the History of Ideas, Vol. 2, p. 65, Charles Scribner's Sons, New York, 1973-1974. Hibat Allah Abu'l-Barakat al-Baghdaadi (1080–1165) wrote a critique of Aristotelian physics entitled al-Mu'tabar, where he was the first to negate Aristotle's idea that a constant force produces uniform motion, as he realized that a force applied continuously produces acceleration, considered "the fundamental law of classical mechanics" and an early foreshadowing of Newton's second law of motion. (cf. Abel B. Franco (October 2003). "Avempace, Projectile Motion, and Impetus Theory", Journal of the History of Ideas 64 (4), p. 521-546 528.) He also described acceleration as the rate of change of velocity.A. C. Crombie, Augustine to Galileo 2, p. 67. The 14th-century philosophers Jean Buridan and Albert of Saxony later refer to Abu'l-Barakat in explaining that the acceleration of a falling body is a result of its increasing impetus. Abu'l-Barakat also modified Avicenna's view on projectile motion, and stated that the mover imparts a violent inclination (mayl qasri) on the moved and that this diminishes as the moving object distances itself from the mover. Abu'l-Barakat also suggested that motion is relative, writing that "there is motion only if the relative positions of the bodies in question change." Averroes (1126–1198) defined and measured force as "the rate at which work is done in changing the kinetic condition of a material body"Ernest A. Moody (June 1951). "Galileo and Avempace: The Dynamics of the Leaning Tower Experiment (II)", Journal of the History of Ideas 12 (3), p. 375-422 375. and correctly argued "that the effect and measure of force is change in the kinetic condition of a materially resistant mass."Ernest A. Moody (June 1951). "Galileo and Avempace: The Dynamics of the Leaning Tower Experiment (II)", Journal of the History of Ideas 12 (3), p. 375-422 380. Newton's third law: law of reciprocal actions Lex III: Actioni contrariam semper et æqualem esse reactionem: sive corporum duorum actiones in se mutuo semper esse æquales et in partes contrarias dirigi. To every action there is always an equal and opposite reaction: or the forces of two bodies on each other are always equal and are directed in opposite directions. A more direct translation than the one just given above is: LAW III: To every action there is always opposed an equal reaction: or the mutual actions of two bodies upon each other are always equal, and directed to contrary parts. — Whatever draws or presses another is as much drawn or pressed by that other. If you press a stone with your finger, the finger is also pressed by the stone. If a horse draws a stone tied to a rope, the horse (if I may so say) will be equally drawn back towards the stone: for the distended rope, by the same endeavour to relax or unbend itself, will draw the horse as much towards the stone, as it does the stone towards the horse, and will obstruct the progress of the one as much as it advances that of the other. If a body impinges upon another, and by its force changes the motion of the other, that body also (because of the equality of the mutual pressure) will undergo an equal change, in its own motion, toward the contrary part. The changes made by these actions are equal, not in the velocities but in the motions of the bodies; that is to say, if the bodies are not hindered by any other impediments. For, as the motions are equally changed, the changes of the velocities made toward contrary parts are reciprocally proportional to the bodies. This law takes place also in attractions, as will be proved in the next scholium.This translation of the third law and the commentary following it can be found in the "Principia" on page 20 of volume 1 of the 1729 translation. In the above, as usual, motion is Newton's name for momentum, hence his careful distinction between motion and velocity. The Third Law means that all forces are interactions, and thus that there is no such thing as a unidirectional force. If body A'' exerts a force on body ''B, body B'' simultaneously exerts a force of the same magnitude on body ''A— both forces acting along the same line. As shown in the diagram opposite, the skaters' forces on each other are equal in magnitude, but act in opposite directions. Although the forces are equal, the accelerations are not: the less massive skater will have a greater acceleration due to Newton's second law. It is important to note that the action and reaction act on different objects and do not cancel each other out. The two forces in Newton's third law are of the same type (e.g., if the road exerts a forward frictional force on an accelerating car's tires, then it is also a frictional force that Newton's third law predicts for the tires pushing backward on the road). Newton used the third law to derive the law of conservation of momentum;Newton, Principia, Corollary III to the laws of motion however from a deeper perspective, conservation of momentum is the more fundamental idea (derived via Noether's theorem from Galilean invariance), and holds in cases where Newton's third law appears to fail, for instance when force fields as well as particles carry momentum, and in quantum mechanics. History of the third law Ibn Bajjah (Avempace) (d. 1138) argued that there is always a reaction force for every force exerted, which Shlomo Pines views as "a precursor to the Leibnizian idea of force" which "underlies Newton's third law of motion",Shlomo Pines (1964), "La dynamique d’Ibn Bajja", in Mélanges Alexandre Koyré, I, 442-468 468, Paris (cf. Abel B. Franco (October 2003), "Avempace, Projectile Motion, and Impetus Theory", Journal of the History of Ideas 64 (4): 521-546 543) though he did not necessarily refer to the reaction force as being equal to the exerted force.Abel B. Franco (October 2003), "Avempace, Projectile Motion, and Impetus Theory", Journal of the History of Ideas 64 (4):521-546 543) His theory of motion had an important influence on later physicists like Galileo.Ernest A. Moody (1951), "Galileo and Avempace: The Dynamics of the Leaning Tower Experiment (I)", Journal of the History of Ideas 12 (2): 163-193 Importance and range of validity Newton's laws were verified by experiment and observation for over 200 years, and they are excellent approximations at the scales and speeds of everyday life. Newton's laws of motion, together with his law of universal gravitation and the mathematical techniques of calculus, provided for the first time a unified quantitative explanation for a wide range of physical phenomena. These three laws hold to a good approximation for macroscopic objects under everyday conditions. However, Newton's laws (combined with universal gravitation and classical electrodynamics) are inappropriate for use in certain circumstances, most notably at very small scales, very high speeds (in special relativity, the Lorentz factor must be included in the expression for momentum along with rest mass and velocity) or very strong gravitational fields. Therefore, the laws cannot be used to explain phenomena such as conduction of electricity in a semiconductor, optical properties of substances, errors in non-relativistically corrected GPS systems and superconductivity. Explanation of these phenomena requires more sophisticated physical theory, including general relativity and quantum field theory. In quantum mechanics concepts such as force, momentum, and position are defined by linear operators that operate on the quantum state; at speeds that are much lower than the speed of light, Newton's laws are just as exact for these operators as they are for classical objects. At speeds comparable to the speed of light, the second law holds in the original form F''' = d'''p/d''t'', which says that the force is the derivative of the momentum of the object with respect to time, but some of the newer versions of the second law (such as the constant mass approximation above) do not hold at relativistic velocities. Relationship to the conservation laws In modern physics, the laws of conservation of momentum, energy, and angular momentum are of more general validity than Newton's laws, since they apply to both light and matter, and to both classical and non-classical physics. This can be stated simply, "Momentum, energy and angular momentum cannot be created or destroyed." Because force is the time derivative of momentum, the concept of force is redundant and subordinate to the conservation of momentum, and is not used in fundamental theories (e.g. quantum mechanics, quantum electrodynamics, general relativity, etc.). The standard model explains in detail how the three fundamental forces known as gauge forces originate out of exchange by virtual particles. Other forces such as gravity and fermionic degeneracy pressure also arise from the momentum conservation. Indeed, the conservation of 4-momentum in inertial motion via curved space-time results in what we call gravitational force in general relativity theory. Application of space derivative (which is a momentum operator in quantum mechanics) to overlapping wave functions of pair of fermions (particles with semi-integer spin) results in shifts of maxima of compound wavefunction away from each other, which is observable as "repulsion" of fermions. Newton stated the third law within a world-view that assumed instantaneous action at a distance between material particles. However, he was prepared for philosophical criticism of this action at a distance, and it was in this context that he stated the famous phrase "I feign no hypotheses". In modern physics, action at a distance has been completely eliminated, except for subtle effects involving quantum entanglement. However in modern engineering in all practical applications involving the motion of vehicles and satellites, the concept of action at a distance is used extensively. Conservation of energy was discovered nearly two centuries after Newton's lifetime, the long delay occurring because of the difficulty in understanding the role of microscopic and invisible forms of energy such as heat and infra-red light. See also * List of scientific laws named after people * Mercury, orbit of * Galilean invariance * Modified Newtonian dynamics * Lagrangian mechanics * Hamiltonian mechanics * Principle of least action * Euler's laws References and notes Further reading & works referred to *Crowell, Benjamin, (2000), [http://books.google.com/books?id=TT4ssKhDdLUC Newtonian Physics], (2000, Light and Matter), ISBN 0-9704670-1-X, 9780970467010, especially at Section [http://books.google.com/books?id=TT4ssKhDdLUC&pg=PA102 4.2, Newton's First Law], Section [http://books.google.com/books?id=TT4ssKhDdLUC&pg=PA106 4.3, Newton's Second Law], and Section [http://books.google.com/books?id=TT4ssKhDdLUC&pg=PA125 5.1, Newton's Third Law]. * * * * *Newton, Isaac, "Mathematical Principles of Natural Philosophy", 1729 English translation based on 3rd Latin edition (1726), volume 1, containing Book 1, especially at the section [http://books.google.com/books?id=Tm0FAAAAQAAJ&pg=PA19 Axioms or Laws of Motion starting page 19]. *Newton, Isaac, "Mathematical Principles of Natural Philosophy", 1729 English translation based on 3rd Latin edition (1726), volume 2, containing Books 2 & 3. *Thomson, W (Lord Kelvin), and Tait, P G, (1867), [http://books.google.com/books?id=wwO9X3RPt5kC Treatise on natural philosophy], volume 1, especially at [http://books.google.com/books?id=wwO9X3RPt5kC&pg=PA178 Section 242, Newton's laws of motion]. * * External links * MIT Physics video lecture on Newton's three laws * Newtonian Physics - an on-line textbook * Motion Mountain - an on-line textbook *Simulation on Newton's first law of motion *"Newton's Second Law" by Enrique Zeleny, Wolfram Demonstrations Project. 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